This invention relates to warewashing machines, and more particularly to compartmentalized warewashing machines of the type having a conveyor which moves food ware items sequentially through the machine from one compartment to the next. Typically such a machine will have a first prewash compartment in which most of the food soil is removed, a main wash compartment in which the remaining food soil is removed, and a rinse compartment wherein fresh water is sprayed on the food ware items to rinse and sanitize them. According to the conditions and needs at hand (e.g., available space, required capacity, and so forth), more or fewer compartments may be provided. Typically, the bottom of each compartment defines a sump which serves as a tank to hold a washing liquid for that compartment. Likewise, each compartment will have a recirculating system consisting of a pump and spray arms for recirculating and spraying the liquid from its respective sump onto the food ware items as they are moved to that compartment by the warewashing machine conveyor. The final rinse, however, will be a fresh water rinse which is not recirculated.
In a typical warewashing machine, at least some of the fresh water from the final rinse is collected in the immediately preceding wash compartment sump, both to refresh the wash water slightly with fresh water, and to make up for water which may have been lost through transport with ware, splash, etc., thereby assuring that the recirculating pump will have an adequate supply and will not cavitate. However, the amount of make-up water is preferably not too great, because it also dilutes the detergent in the sump, which typically has an overflow drain communicating with the sump next upstream, such as the prewash sump. The overflow drain provides a steady supply of liquid to the prewash sump for substantially the same reasons that rinse water is collected in the main wash sump. Since the largest quantity of food soil debris is removed in the prewash compartment, its liquid tends to be the most soiled. The liquid in each subsequent compartment tends to be cleaner since there is less and less food soil debris to remove at each subsequent washing stage. Thus, the overflow drains cascade the surplus water sequentially from the cleanest sumps to those having the most debris.
It is important that the liquid in each sump have as little food soil debris therein as possible. This is important not, as might be initially thought, for removing the food soil debris from the food ware the mechanical action of striking the dishes with the high pressure liquid will remove the debris whether or not there is debris already suspended in the liquid. Rather, when debris is suspended in the wash liquid some of it tends to redeposit onto the food ware items and must again be rinse off. The more soiled the water, the greater the redeposit. Therefore, the liquid in each compartment is usually strained to reduce the amount of suspended debris therein. However, filtration removes only the larger food soil particles. Minute particles, such as mashed potatoes, gravies, bread stuffs, etc., usually go into suspension and cannot be economically filtered. The use of several distinct washing compartments, therefore, which progressively have less and less suspended food soil debris, is to reduce the amount of redeposited food soil as the food ware items progress through the ware washing machine. The "upstream" cascading of the make-up liquid from one compartment to another is also arranged for the same purpose.
If water and detergent were free and available in unlimited quantities, redeposit would never occur because the liquid would never have to be recirculated. Production machines, of course, must represent a compromise in which the best washing results are sought to be accomplished with the least consumption of water, detergent, energy, space utilization, and so forth. Accordingly, in addition to the features discussed above, many conveyor type warewashing machines have splash curtains which are hung across the openings which separate and connect one compartment from another, to discourage and substantially prevent the liquid spray in one compartment from entering the other. Of course, the curtains must yield to food ware as it is moved therethrough by the conveyor, so in some machines the compartments are separated by a zone which serves as a watershed to return those sprays which evade the curtain. The longer the zone, the better the separation, but also the larger the warewashing machine. Since space is at a premium, especially in commercial applications, and since longer spaces may not be available for such machines in many locations, longer chamber separation zones are a solution with only limited appeal.
When the chambers are adjacent one another, a splash curtain helps but is not a complete solution. Splashover of the spray from one compartment into the next will still occur by rebounding of the liquid from the conveyor drive mechanism, racks and rack tracks (if the food ware items are transported in racks), the food ware items themselves, and even the splash curtains when the food ware items and/or racks push the curtain bottom over into the next compartment as the conveyor moves them therepast. Similarly, flow configurations within a given compartment, perhaps necessitated by overall machine design constraints, may cause liquid to pool at the opening between the compartments, such that some of it will escape into the adjacent compartment beneath the splash curtain.
A need thus remains for a system for use in a warewashing machine which will improve the isolation of the liquid in one compartment from the next while providing for minimum (ideally zero) separation therebetween. By improving the isolation, the make-up liquid required for each compartment and the detergent required for the wash compartments are reduced, not only because less food soil debris will be transported into the compartment from the more soiled compartments upstream, but also because the amount of liquid lost by one compartment to the next will be reduced so that there will be less tendency of the recirculating pump to cavitate, and hence less precautionary make-up liquid will be required. The improved isolation should also be maintained even while food ware items are being transported through the opening from one compartment to the next, and displacing the splash curtain.